5 Best Acura RSX Engine Mods

5 Best Acura RSX Mods

Chandler Stark

Meet Chandler

Chandler is an automotive expert with over a decade of experience working on and modifying cars. A couple of his favorites were his heavily modded 2016 Subaru WRX and his current 2020 VW Golf GTI. He’s also a big fan of American Muscle and automotive history. Chandler’s passion and knowledge of the automotive industry help him deliver high-quality, insightful content to TuningPro readers.

From 2002-2006, the Acura RSX and its performance Type-S variant were two of the most fun cars you could buy. Moderately priced and boasting decent performance, Acura powered the RSX and Type-S with various iterations of the Honda K20 motor. Honda/Acura enthusiasts have long praised the K20 engine for being easy to mod and able to reliably handle power. From the factory, Acura rated the standard RSX at 160 horsepower and 142 lb-ft of torque, and put the RSX Type-S at 200-210 horsepower and 142-143 lb-ft of torque.

While the RSX and Type-S perform admirably stock, they really do well with a few mild engine and suspension mods. Especially considering the cars are coming up on two decades of age, a few performance RSX mods are almost necessary to keep pace with more modern cars. Adding bolt-ons to the engine and suspension are a cost-effective way to increase performance while staying reliable on the RSX.

This guide will cover the 5 Best Acura RSX mods for both the standard and Type-S models. First we’ll go over the basics behind the differences between the two suspension and engine wise, before we get into the best RSX mods for your build. First, let’s start with the basic story of the RSX and Type-S in the U.S..

5 Best Acura RSX Engine Mods
Credit: Motortrend

Acura RSX History

Acura introduced the RSX and Type-S to the U.S. market in 2002 as the successor to the outgoing third generation DC5 Acura Integra. The RSX is considered the fourth generation (DC5) of the Integra, even though Acura badged it differently. In the Japanese and Australian markets, it was sold under the Honda Integra name.

There were three main variants of the RSX; the standard RSX, Type-S, and Type-R. The USDM market only got the standard and Type-S models. For its entire 2002-2006 USDM run, Acura put the K20A3 inline-four engine inside the base RSX, rated at 160 horsepower and 142 lb-ft of torque. From 2002-2004, Acura gave the Type-S the K20A2 motor, where it made 200 horsepower and 142 lb-ft of torque.

From 2005-2006, the Acura RSX Type-S used the upgraded K20Z1 engine. In 2005, Acura rated the engine at 210 horsepower and 143 lb-ft of torque, but in 2006 advertised power dropped to 201 horsepower. While some think this means the 2006 Type-S is less powerful, that’s actually not the case. In 2006, Acura adopted the SAE’s new regulations for rating horsepower, which caused a drop on paper to 201 horsepower for the K20Z1. The 2005 Type-S also would have made 201 horsepower according to the new SAE method.

Acura discontinued the Integra/RSX line after the 2006 model year worldwide. They have only recently resurrected it for the upcoming 2023 model year, featuring a completely new engine and chassis.

Acura RSX Engines

Before we get into the best RSX mods, first let’s look at the various engines inside the standard and Type-S. For its entire run the base RSX used the K20A3, the 2002-2004 Type-S used the K20A2, and the 2005-2006 Type-S used the K20Z1. All of these engines are naturally aspirated and part of the K20 engine series. They are all relatively similar internally.

K20A3 vs K20A2 Engines

All K20 motors have 2.0 L (1,998 cc) of displacement and have an inline-four configuration. The K20 series has a bore and stroke of 86 mm x 86 mm, making it a perfectly square engine. Both the RSX and Type-S engines are DOHC and have VTEC, Honda’s famous proprietary VVT system. Honda rated the K20A3 at 160 horsepower and 142 lb-ft of torque, the K20A2 at 200 horsepower and 142 lb-ft of torque, and the K20Z1 at 201-210 horsepower and 143 lb-ft of torque.

The K20A2 is essentially a performance version of the K20A3. It has a higher compression ratio of 11.0:1 over 9.8:1, which is due to a new cylinder head and higher compression pistons. Honda gave the K20A2 a balanced crankshaft, as well as dual valve springs for the upgraded i-VTEC system. The K20A2 also has a higher red line at 7,900 RPM vs 6,800 RPM, and has more aggressive camshafts and a higher flowing PRB intake manifold.

The K20A3 has VTEC-E, but only for the intake cams, and mainly uses it for fuel efficiency and emissions reduction rather than optimizing horsepower. The K20A2 has Honda’s i-VTEC system, a system that utilizes both intake and exhaust cams and is designed for increased horsepower. Here is a good breakdown of the VTEC-E vs i-VTEC systems.

The K20Z1 Engine

The K20Z1 engine has the same displacement and sized block as the K20A3/2. It has the same PRB intake manifold as the K20A2, and the same 11.0:1 compression ratio, but has a new exhaust manifold and even more aggressive camshafts. Honda bumped the red line on the K20Z1 even higher than the A2, up to 8,100 RPM with an 8,300 RPM rev limiter. Like on the K20A2, the K20Z1 i-VTEC engages at 5,800 RPM.

Top 5 Best Acura RSX Mods

5 Best Acura RSX Engine Mods
Credit: DSport Magazine

The top 5 best Acura RSX mods are (including Type-S):

  • Cold Air Intake
  • Exhaust Header and Cat-back Exhaust
  • ECU Tuning
  • Sway Bar
  • Forced Induction

Now let’s get into the 5 best mods for your Acura RSX and RSX Type-S. We kept the list to basic bolt-on engine and suspension upgrades to maximize cost effectiveness. This is by no means an exhaustive RSX mods list, but is a good intro path to starting your K20A/Z build.

Unfortunately, with time the RSX has become less popular and as a result there is not nearly the aftermarket community there once was. By 2022, most of the popular and highest reviewed manufacturers from the heyday of the RSX in the early-2000s, like Comptech, Greddy, and Cybernation Motorsports, are no longer making parts for the car.

Still, there is a decent RSX mods community out there building and racing K20 powered DC5 Integras. Depending on which RSX engine you start with, you can add 20-35 wheel-horsepower with full bolt-ons. While we won’t go over it in depth, swapping on a Type-S intake manifold and cylinder head to a standard RSX is also a very common mod that nets decent gains, too.

Best Acura RSX Mod 1: Cold Air Intake

By far the most popular mod for the Acura RSX and Type-S is a cold air intake. Not only are they relatively cheap, but they provide a decent performance gain on a naturally aspirated engine. There are two kinds of RSX intakes, either short ram or cold air. We 100% recommend the cold air over the short ram.

The short ram RSX intakes barely relocate the filter from where the stock airbox is, and they are very prone to heat soak. In contrast, RSX cold air intakes instead relocate the filter to very low in the engine bay. Instead of taking air from the top of the bay where it’s very hot, instead the filter is routed to take air from behind the fog light grill area on the driver’s side. It is one of the rare true cold air intakes for modern cars.

The top benefits from a cold air intake are:

  • +5-15 horsepower
  • Improved throttle responsiveness
  • Increased engine noise
  • Improved fuel economy

After installing a cold air intake, you should see gains of 5-15 horsepower and the car will feel more responsive on the throttle. Relocating the filter brings in cooler air, which increases oxygen content and thus horsepower. The tubing is also much less restrictive and optimized for the best flow.

In addition to the increased power, you’ll also definitely hear your intake much louder than before. The whooshing sound of air being sucked in will be much more prominent, and proof your intake is working.

Finally, though it will be minimal, you’ll also see a mild improvement in fuel economy. The colder air allows the engine to work more efficiently, allowing it to make the same power with less fuel. The difference will probably only be 0.5-1.5 MPG difference, but it adds up over time.

RSX Intake Hydrolock Concerns

When upgrading to a cold air intake, you have to be cognizant about the potential for hydrolocking. Hydrolocking occurs when the air filter becomes so wet that it actually sucks water into the combustion chamber. An engine will fail to compress and spark correctly once water enters, which can lead to big consequences for your internals.

Some people will say that most upgraded RSX cold air intakes sit too low and risk hydrolock, while others say it’s not a big deal. Generally speaking, unless you totally submerge the air filter in water, like driving over a flooded area, you will probably not have to worry. However, if you find yourself consistently driving in flooded or very wet areas, you might need to consider a short ram.

Top RSX Intakes

In the RSX community, by far the most popular intakes are the AEM, Injen, and Comptech IceBox. The Comptech IceBox was one of the most used intakes of them all, but it has been discontinued for years.

That means the real competition is between the AEM and Injen cold air intakes. Both of them also offer short ram versions, but as we said before we definitely recommend the cold air versions. Of the two, we suggest the AEM RSX intake. It has dyno proven performance and is very easy to install.

One important thing to keep in mind is that when you install the AEM cold air intake, you will have to relocate the stock windshield wiper reservoir. This is because the filter sits where the stock reservoir is, which allows it to get as cool air as possible. It’s not very hard to relocate it and AEM includes a new reservoir, but it’s something to keep in mind.

Purchase Link: AEM RSX Cold Air Intake

Best Acura RSX Mods 2: Header and Exhaust

After upgrading to a cold air intake, the next step for most RSX builds is to upgrade the header and exhaust. There are two kinds of header for the RSX, a race header and shorty header. The race header makes more power than the shorty header, because race headers eliminate the catalytic converters.

Race headers are not street legal in most places because they are catless, making shorty headers many people’s only option. After upgrading the header, the cat-back portion of the exhaust is also ripe for an upgrade.

Top RSX Header and Exhaust Benefits:

  • +15-25 horsepower (race header)
  • Increased exhaust flow
  • Increased exhaust sound
  • Reduced back pressure

Upgrading the header will net between 15-25 horsepower on the K20 powered RSX and Type-S. An upgraded header will have larger diameter piping, which equates to increased exhaust flow, reduced back pressure, and increased exhaust scavenging. Your engine will be able to breathe easier and expel exhaust quicker with upgraded headers.

Getting a larger cat-back exhaust won’t have the same effect on power as the header, but it will definitely increase exhaust volume and improve the tone. Importantly, most race headers will not connect to the stock exhaust, making a new cat-back or adaptor necessary.

Best RSX Header and Exhausts

There are many different choices for upgrading the K20 header. We’re going to recommend the Private Label Manufacturing RSX race header. Their header is catless, 2.5” in diameter, uses 304SS, and has a CNC machined flange. As far as current RSX headers, it is the top one on the market.

Previously, the DC Sports Race header was the top of the line, but they only make a shorty version now. However, their shorty version is CARB compliant, making it 50 states emissions legal.

The header we would recommend is from CompTech, but unfortunately it is no longer in production. We would suggest staying away from the Skunk 2 Alpha header, as it has very known fitment and quality issues.

As for the exhaust, the DC Sports cat-back and HKS cat-back are considered the RSX standards. They both produce excellent volume and tone and are known for good fitment and easy installation.

Purchase Links:

DC Sports RSX Shorty Header

Private Label Manufacturing RSX Race Header

Best Acura RSX Mods 3: ECU Tuning

Now that you have upgraded the intake, header, and exhaust, your next step is to look into RSX ECU tuning. The ECU determines basically every function of how the RSX engine operates, including its performance. By upgrading the RSX’s stock ECU tuning, you can add horsepower, torque, improve the power band, and optimize your mods.

The purpose of the upgraded intake and exhaust is to push more air in and then out of your engine at the highest velocity possible. Tuning helps you get the most out of these upgrades by optimizing parameters like ignition timing, cam timing, and air-to-fuel ratios. You can expect a 15-20% increase in performance from your mods after ECU tuning.

Best RSX ECU Tuning Options

For the RSX, there are really only two options for basic tuning, the Hondata KPro and the KTuner. They both do pretty much the same exact thing and have very similar features. The KTuner offers a little more customization than the KPro, but more tuners are familiar with the KPro in general.

Really, for most people the choice comes down to cost. For the 2002-2004 RSX and Type-S, the KPro is cheaper to use. For the 2005-2006 RSX and Type-S, the KTuner is the cheaper option. This is because the KPro can work with the ‘02-’04 ECU without modification, but not the ‘05-’06 ECU. Comparatively, the KTuner works with the ‘05-’06 ECU without modification, but not the ‘02-’04 ECU.

The other option for RSX tuning is to get a complete standalone system like a Haltech or AEM EMS. But these are pretty serious and much more expensive upgrades. For pretty much all moderate builds, a KPro or KTuner will be sufficient.


Hondata KPro RSX ECU Tuner

KTuner RSX ECU Tuner

Best Acura RSX Mods 4: Upgraded Rear Sway Bar

Now that we have looked at upgrading the engine with some basic bolt-ons, your next concern should be the car’s handling. From the factory, the RSX is known for having a woefully inadequate suspension setup. While a lot of people start with lowering springs or coilovers, we’d suggest first looking at getting a bigger rear sway bar.

The purpose of the sway bar, also known as an anti-roll bar, is to connect the left and right side of the suspension together. As a car turns, the weight transfers from both wheels to mainly the outside wheel. The purpose of the sway bar is to clamp down on the springs on the inside wheel, keeping the car level and stopping body-roll.

The stock sway bar and rubber bushings are barely adequate for the stock power levels, so when you start adding more they are completely overmatched. Switching to a stiffer and stronger sway bar with better bushings will prevent body roll. A larger size will help with overall stability.

Best RSX Rear Sway Bars

The factory RSX sway bars are between 18-21 mm, most people upgrade to something 22-24 mm. There are tons of different sway bar options out there, and most of them perform pretty much the same. You can always get one of the top brand names like Eibach, Whiteline, or Cusco, but we recommend the Progress rear sway bar.

The Progress rear sway bar is 24 mm and has a brace and adjustable end links, as well as strong polyurethane bushings. It will definitely provide better traction when going through turns, and is also noted for its quietness.

Many sway bars, especially adjustable ones, will pop and bang after being installed, but the Progress is very mild. If you’ve already upgraded some bolt-ons, you’ll definitely want a stiffer rear sway bar before adding anything else.


Progress RSX Rear Sway Bar

Best Acura RSX Mods 5: Forced Induction

For our final recommendation, we’re going with the heavy hitter: forced induction. To be clear, a turbo or supercharger is far from the first mod you will want to do. However, the K20A/Z engines inside the RSX are pretty limited in what you can achieve power-wise with just bolt-ons. There is only so much the K20 motors can do with natural aspiration. If you want decent power, you will need to add some kind of blower.

There is a lot of debate about how much the stock engine can handle, but the consensus is generally that they can support quite a bit of power. There are some supposedly stock K20A/Z motors making over 500 wheel-horsepower with stock internals and stock block. For us, we’d say 450 horsepower is probably closer to the limit before you will want to add forged pistons, rods, and head studs for reliability.

Top RSX Turbo Kits

The most popular turbo kits from the RSX’s heyday in the early-2000s; Greddy, Cybernation, HKS, RevHard, and Full Race; are now all long discontinued and out of production. Instead, we have two recommendations: CX Racing’s turbo kit, or a custom created turbo kit from Full Race.

The CX Racing’s RSX turbo kit has a GT35 turbo with a T3 housing. It is capable of up to 450 horsepower and comes with a bar and plate style intercooler, as well as all intercooler piping and a downpipe.

Full Race has turbos, intercooler piping (charge pipes), intercoolers, exhaust manifolds, and more for the K20 series engine. It will undoubtedly be more expensive to build your own kit through Full Race, but it will be much higher quality than the CX Racing kit. In addition, you can pick and choose parts from the Full Race kit to combine with custom fab parts to cut down on costs.

Keep in mind, the different K20s inside the different model/years of the RSX have different compression ratios. While the K20Z1 makes the most horsepower, it also has the highest compression ratio (along with the A2 at 11.0:1). The K20A3 9.8:1 is a much better ratio for boosted motors, but it’s also the least powerful from the factory.

The K20Z1/A2 still does pretty well, but it’s something to keep in mind. Getting pistons with different compression ratios is one option that can help.


CX Racing RSX K20 Turbo Kit

Full Race RSX Custom Turbo Kit Components

Acura RSX Best Mods Summary

While the Acura RSX and RSX Type-S is not a performance machine from the factory, a few tasteful engine and suspension bolt-ons can really wake it up and make it perform on par with much newer cars. The K20 engine is one of the best Honda engines ever created, and all three iterations in the RSX respond to bolt-ons.

Whether you are looking for a few extra horsepower to make getting on the interstate and merging a little easier, or you want a full blown 450 horsepower monster RSX terrorizing the streets, this guide can help you get there. Don’t forget to upgrade the suspension too, or your newly powerful RSX will be hard to handle.

Let us know about your K20 powered RSX experience below!

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